Electric drives are used to control the phase currents of electric motors. In a digitally-controlled system, multiple phase currents typically are sampled simultaneously and converted into digital values using analog-to-digital (A-to-D) converters. These digital values are provided to a system controller, which may adjust the phase currents according to the digital values.
In some systems, multiple analog-to-digital (A-to-D) converters may be used simultaneously to sample the multiple phase currents. For example, in a system which provides three-phase current, three A-to-D converters may be implemented in parallel sampling channels. The sampling instants for each phase current typically are controlled with precision, which may enable detection and reduction of aliasing that may be introduced by phase ripple current.
In some cases, fewer A-to-D converters may be available than the number of phase currents. For example, the system may include fewer A-to-D converters than the number of phase currents or the system may, at various times, use one or more of the A-to-D converters normally used for sampling phase currents for other purposes. At these times, the system controller may not receive a sampled current value for each phase current, and accurate control of the phase currents may be compromised. The sampling errors introduced may be reflected back into the phase currents, resulting in significant torque ripple, current harmonics, and/or other undesirable artifacts that may detrimentally affect the performance of the electric motor.
Accordingly, it is desirable to provide apparatus and methods for sampling phase currents of an electric motor that may use fewer A-to-D converters than the number of phase currents, where the apparatus and methods introduce less torque ripple, current harmonics, and/or other undesirable artifacts that may be introduced using conventional apparatus and methods. Furthermore, other desirable features and characteristics of the inventive subject matter will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.